THURSDAY, Sept. 1 HealthDay News) -- After rising steadily through the 1990s, the rate of circumcisions for newborn American boys has waned a bit over the past decade, a new report shows.

According to the U.S. Centers for Disease Control and Prevention (CDC), circumcisions among newborn males dropped from 62.5 percent in 1999 to just under 57 percent by 2008. That data came from the National Hospital Discharge Survey, and was corroborated by similar results from other nationwide sources.

"Newborn male circumcision levels in the U.S. remain relatively high, but have declined slightly," said agency spokesman Scott Bryan.

The report examines trends in newborn circumcision in hospitals, and therefore underestimates the overall level of newborn circumcision, Bryan noted. "The results of the analysis indicate that approximately 55 to 57 percent of males born in hospitals are now being circumcised there," he said.

The recent drop in the circumcision rate reverses a trend of the late 1980s and 1990s, when the procedure rose from about 48 percent of newborn boys (in 1988-1991) to over 61 percent (in 1997-2000).

The CDC doesn't have a definitive answer as to what's behind the recent decline. According to Bryan, changes in parental preferences and the fact that many state Medicaid plans do not cover the procedure could play roles.

"In fact, a recent study found that, after controlling for other factors, hospitals in states in which Medicaid covers routine male circumcision had circumcision rates that were 24 percentage points higher than hospitals in states without such coverage," Bryan noted.

The longstanding controversy over circumcision of newborns has heated up recently, with opponents claiming it is not medically justified and can lead to mental health issues later in life.

On Wednesday, the California Senate passed a bill preventing cities in that state from banning newborn circumcisions. The move came after a controversial ballot initiative, begun earlier this year in San Francisco, which would have banned circumcision in that city for people under the age of 18. A judge in July ruled against the proposal and it was struck from the ballot.

Dr. Jeff Brosco, a professor of pediatrics at the University of Miami Miller School of Medicine, said that "there is some evidence that circumcision improves the health of boys."

Some of the benefits of circumcision include helping to prevent urinary tract infections and making it less likely to transmit sexually transmitted diseases, Brosco said. "But the evidence is not so strong that we routinely recommend it," he added. "It's really up to families."

As far as the critics of circumcision go, Brosco said "there is no evidence that there are real dangers associated with circumcision," he said. "In the long-term the benefits seem to outweigh the risks," he added.

However, Brosco agreed that there is no health effect on the infant if he is not circumcised.

The report was published in the Sept. 2 issue of the CDC's Morbidity and Mortality Weekly Report.